1. Field of the Invention
This invention relates to Tumor Necrosis Factor Receptor Super Family 25 (TNFR25) agonists, immunotoxins, antagonists and their use in treating cancer, inflammation and effecting immunosuppression, respectively.
2. Background
Many disorders of the human immune system fall into two broad categories: those characterized by an attenuated immune response and those characterized by overzealous immune responses. Immunodeficiency is characterized by an attenuated response. There are congenital (inborn) and acquired forms of immune deficiency. Chronic granulomatous disease, in which phagocytes have trouble destroying pathogens, is an example of the former. AIDS (“Acquired Immune Deficiency Syndrome”), an infectious disease, caused by the HIV virus that destroys CD4+ T cells, is an example of the latter. An additional disease that may be characterized by an attenuated immune response is cancer. In contrast to healthy individuals, cancer patients' immune systems are no longer capable of effectively recognizing and/or destroying tumor cells.
Despite high hopes, there are no medications to date that directly increase the activity of the immune system. However, biological therapies have recently been used to recruit the immune system, either directly or indirectly, to fight diseases such as cancer. Monoclonal (MAb) antibodies are now frequently used as a biologic therapy. For example, monoclonal antibodies may react with specific types of cancer cells, and have direct or indirect antitumor effects.
Tumor vaccines may be employed therapeutically or for prophylaxis after primary therapy. Anti-tumor vaccines may need to induce cellular immunity in the form of tumor-specific cytotoxic T cells of the CD4 or CD8 phenotype. It is thought that effective anti-tumor immunity requires the generation and maintenance for long periods of times of such cytotoxic cells. In addition evidence indicates that the innate arm of the immune system must be activated in order to generate effective anti-tumor vaccines. Vaccines that enhance or generate humoral responses produce antibodies that can be detected over a relatively long period. To be effective, these antibodies need to be capable of targeting cell surface antigens in live cell assays. Maintaining specific cellular immune responses to antigen epitopes (adaptive immunity) may require more frequent immunizations, although memory cells can sustain the ability to respond and rechallenge the immunizing epitope. As such, it would of substantial benefit to have access to therapies that would be capable of boosting cancer specific cellular immune responses to tumor vaccines.
On the other end of the scale, an overactive immune system figures in a number of other disorders, particularly autoimmune disorders such as lupus erythematosus, type I diabetes (sometimes called ‘juvenile onset diabetes”), multiple sclerosis, psoriasis, rheumatoid arthritis and inflammatory bowel diseases such as Crohn's Disease and ulcerative colitis (UC). In these, the immune system fails to properly distinguish between self and non-self and attacks a part of the patient's own body. Other examples of overzealous immune responses in disease include hypersensitivities such as allergies and asthma.
Suppression of the immune system is often used to control autoimmune disorders or inflammation when this causes excessive tissue damage. Immunosuppressive medication intentionally induces an immunodeficiency in order to prevent rejection of transplanted organs. Commonly used immunosuppressants include glucocorticoids, azathioprine, methotrexate, cyclosporin, cyclophosphamide and mercaptopurine. In organ transplants, selective T cell inhibition prevents organ rejection, and cyclosporin, tacrolimus, mycophenolate mofetil and various others are used.
T lymphocytes play a central role in regulating immune responses. Helper T cells express the CD4 surface marker and provide help to B cells for antibody production and help CD8 T cells to develop cytotoxic activity. Other CD4 T cells inhibit antibody production and cytotoxicity. T cells regulate the equilibrium between attack of infected or tumorigenic cells and tolerance to the body's cells. A disregulated immune attack can lead to autoimmunity, while diminished immune responsiveness results in chronic infection and cancer.
Tumor Necrosis Factor Receptor 25 (TNFR25) also interchangeably referred to herein as Death receptor 3 (DR3), as discussed herein, is a regulator of T cell function. Death receptor 3 (DR3) (Chinnaiyan et al., Science 274:990, 1996) is a member of the TNF-receptor family. It is also known as TRAMP (Bodmer et al., Immunity 6:79, 1997), wsl-1 (Kitson et al., Nature 384:372, 1996), Apo-3 (Marsters et al., Curr Biol 6:1669, 1996), and LARD (Screaton et al., Proc Natl Acad Sci USA 94:4615, 1997) and contains a typical death domain. Transfection of 293 cells with human DR3 (hDR3) induced apoptosis and activated NF-KB. The cognate ligand for DR3 has recently been identified as TL1A (Migone et al., Immunity 16:479, 2002) and has been shown to have costimulatory activity for DR3 on T cells through the induction of NF-KB and suppression of apoptosis by expression cIAP2 (Wen et al., J Biol Chem 25:25, 2003). TL1A also binds to the decoy receptor 3 (DcR3/TR-6), indicating that fine-tuning of biological TL1A accessibility is of critical importance. Multiple spliced forms of human DR3 mRNA have been observed, indicating regulation at the post transcriptional level (Screaton et al., Proc Natl Acad Sci USA 94:4615, 1997).
Many TNF-receptor family members have the ability to induce cell death by apoptosis or induce costimulatory signals for T cell function. The regulation of these opposing pathways has recently been clarified for TNF-Rl, the prototypic death domain-containing receptor that can cause apoptosis or proliferation of receptor positive T cells (Micheau and Tschopp, Cell 114: 181, 2003). NF-KB activation by a signaling complex composed of TNF-Rl via TRADD, TRAF2 and RIP induces FLIPL association with a second signaling complex composed of TNFRI, TRADD and FADD, preventing caspase 8 activation as long as the NF-KB signaling persists. DR3 has been shown to be able to induce apoptosis in transfected cells and to induce NF-KB and all three MAP-kinase pathways (Chinnaiyan et al., Science 274:990, 1996; Bodmer et al., Immunity 6:79, 1997; Kitson et al., Nature 384:372, 1996; Marsters et al., Curr Biol 6:1669, 1996; Screaton et al., Proc Natl Acad Sci USA 94:4615, 1997; Wen et al., J Biol Chem 25:25, 2003). Blocking of NF-KB, but not of MAP-kinase and inhibition of protein synthesis resulted in DR3-mediated cell death, indicating that NF-KB signals mediate anti-apoptotic effects through the synthesis of anti-apoptotic proteins.
Expression of human DR3 mRNA is pronounced in lymphoid tissues, mainly in the spleen, lymph nodes, thymus, and small intestine, indicating an important role for DR3 in lymphocytes. Murine DR3 has been deleted by homologous recombination in embryonic stem cells (Wang et al., Mol Cell Biol 21:3451, 2001). DR3−/− mice show diminished negative selection by anti-CD3 in the thymus but normal negative selection by superantigens and unimpaired positive selection of thymocytes. Mature peripheral T cells were unaffected by DR3 deficiency. Despite a significant amount of preliminary research, the physiological function of DR3 remains poorly characterized.
All scientific publications including patent documents cited herein are incorporated by reference in their entirety for all purposes.